DESCRIPTION: This proposal focuses on the mechanism of cytokinesis and cortical flow in Xenopus oocytes. The applicant's group reported the finding that treatment of frog oocytes/eggs with the phorbol ester, PMA, leads to cortical contraction and the formation of cleavage furrows. Using this cortical activity as a model, Dr. Bement proposes to investigate the regulation of reorganization of the actin cytoskeleton in the cortex during cell cleavage. He provides considerable amounts of preliminary data including the important observation that the cortical flow appears to be directly related to the level of microtubule polymerization and depolymerization. In order to evaluate the role of microtubule involvement in the process of actin/myosin rearrangement, Dr. Bement proposes following three specific aims: 1) microtubule effects on myosin assembly will be monitored by both sedimentation analysis and microscopy. The level of myosin phosphorylation will be compared with its ability to form aggregates under the condition to stimulate microtubule disassembly. 2) The process of myosin reorganization will be repeated in a cell free system using frog egg extracts. 3) Cytoskeletal reorganization during cortical flow will be monitored by immunofluorescence and confocal microscopy. 4) Finally, he will determine the effect of MAPs on cortical flow by identifying Xenopus MAP(s).